Process of impregnating vulcanized foam rubber with an aqueous dispersion comprisingcolloidal silica



March 1, 1960 A. TALALAY ET AL 2,926,390

PROCESS OF IMPREGNATING VULCANIZED FOAM RUBBER WITH AN AQUEOUSDISPERSION COMPRISING COLLOIDAL SILICA Filed July 25, 1956 2Sheets-Sheet l ESVEIHONI BQNVJSISEIH NOISSHZ-JdWOO INVENTORS ANSELMTALALAY WILLIAM D.COFFEY BY JOSEPH ATALALAY ATTY.

FIG. I

March 1960 A. TALALAY ET AL 2,926,390

PROCESS OF IMPREGNATING VULCANIZED FOAM RUBBER WITH AN AQUEOUSDISPERSION COMPRISING COLLOIDAL SILICA Flled July 25, 1956 2Sheets-Sheet 2 COMPARISON OF 3.25"THK. UTILITY CORED FOAM UNTREATED VS.TREATED DEF LECT ION INVENTORS ANSELM TALALAY WILLIAM D.COFFEY BY JOSEPHA.TALALAY FIG. 2 j fl AT T Y.

of the polymer in the latex.

United States Patent PROCESS or IMPREGNATING VULCANIZED FOAM RUBBER WITHAN AQUEOUS DIS- PERSION COMPRISING COLLOIDAL SILICA Application July 25,1956, Serial No. 600,015 19 Claims. (Cl. 18-53) This invention relatesto a process for making latex foam rubber and pertains more particularlyto a method for making latex foam rubber wherein the vulcanized foamrubber istreated with an aqueous dispersion comprising colloidal silicato increase the compression resistance or load-bearing capacity of thefoam rubber. This application is a continu'ationdn-part application ofour application Serial No. 366,561, filed July 7, 1953.

In the commercial manufacture of foam rubber, a latex compounded withsuch'materials as vulcanizing agents, accelerators and antioxidants isfrothed either by mechanically entraining air in the latex. orby'causing the release of a gas within the latex{ The frothed latex thenis congealed or gelled by any of a'variety of known ways andtheco'ngealed cellular'rriassfis vulcanized, washed and dried. Theresulting foam rubber has ari open-cellstructure (a structurewhichconsists of a network of'inte'r'c'onnecting cells), and isextensively used in the manufacture ofpillows, seat cushions, mattressesand the like. i

Foam rubber usually is graded according to its compression resistancewhich commercially is determined by measuring the force required tocompress (with a circular disk 50 square inches in area) a foam rubbersample to 75 percent of its original height. (This method fordetermining the compression resistance of a foam rubber is described inBuyers Specification-Latex Foam, issued by The Rubber ManufacturersAssociation, Inc.,-and in A.S.T.M. Specification designation D4055). Formost uses of foam rubber, it is desirable that the compressionresistance of the foam rubber be'as high as possible for a given unit ofweight since the load-carryingcapacity of a foam rubber is improved whenthe compression resistance of the foam rubber is increased.

The compression resistance of foam rubber largely is a function of itsdensity and the modulus of elasticity It has been reported in thearticle by Joseph A. Talalay appearing in Industrial and EngineeringChemistry, volume 46, pages 1530-1538 (1954), that the change incompression resistance of foam rubber with density can be expressed bythe formula:

h=4(1-) /P where 0=(lG',/0.034) where h is the force in pounds persquare inch required to compress the foam rubber to 75 percent of itsoriginal height, G; is the density of the foam rubber in pounds aqueousdispersion of a 2,926,390 Patented Mar. 1, 1950 2 per' cubic inch, and Pis a parameter'in square inches per pound. It was found also that thecompression resistance of foam rubber is affected somewhat by the sizeand shape of the cells of the foam rubber.

While the compression resistance of sponge rubber (expanded dry rubber)can be varied over a wide range by judiciously compounding the dryrubber with finelydivided reinforcing materials such as carbon blacksand fine particle clays, the properties of a rubber product formeddirectly from a latex can not be improved appreciably by the addition ofcompounding materials to the latex. pression resistance of a foam rubbercan be obtained by adding moderate amounts of materials such as claysand hydrated alumina to the latex, other physical properties of the foamrubber usually are adversely afiected by the addition of suchjmaterialsto the latex. Consequently, improving the compression resistance of foamrubber by judicious compounding of the latex is unsatisfactory.

It now has been found that if a vulcanized open-cell foam rubber isimpregnated with an aqueous dispersion or suspension comprisingcolloidal silica, the compression resistance of the dried foam rubber isunexpectedly increased while the other physical properties of the foamrubber are relatively unaffected. The effect of the treatment of a foamrubber with an aqueous colloidal silica dispersion is illustrated in thedrawings in which:

Fig'. 1 is a graph illustrating the increase in compression resistanceobtained when a foam rubber is made in accordance with this invention;and P Fig. 2 is a graph illustrating the improved compression resistanceproperties of a foam rubber made by the process of this invention ascompared with a foam rubber which has not been treated with an aqueouscolloidal silica dispersion as hereinafter described; I In accordancewith the process of this invention, the latex is compounded in the usualmanner with materials normally added to the latex to form a latexcomposition suitable'for making foam rubber. The latex maybea naturalrubber latex (which essentially is an polymer of isoprene), or asynthetic rubber latex, such as an aqueous dispersion of a rubberypolymer of an open-chain conjugated diolefin-having from four to eightcarbon atoms exemplified by butadienel,3; l,4-dimethyl butadiene-l,3;2,3- dimethyl butadiene-l,3, and the like, or of rubbery copolymers ofsuch diolefins and similar conjugated diolefins with each otheror withcopolymerizable monomeric materials containing a single ethyleniclinkage exemplified by styrene, methyl acrylate, methyl methacrylate,ethyl acrylate, ethyl methacrylate, acrylonitrile, or similar materials,or of rubbery polymers of chloroprene and the like, or a blend of anatural latex with a synthetic latex or a blend of synthetic lattices.

The compounded latex is frothed or foamed, for example, by mechanicallyentraining a non-coagulating gas such as air or nitrogen in the latexuntil the volume of the froth is suflicient to form a foam rubber of adesired density or by adding to the latex a gas-liberating materialwhich decomposes in the latex or chemically reacts with another materialin the latex with the evolu: tion of a gaseous product in the latex, andthe frothed or foamed latex is congealed or coagulated. GelationAlthough a slight improvement in the com- 3., of the frothedlatexcanbeaccomplished by adding a delayed action coagulant such as sodiumsilicofluoride," potassium silicofluoride, ammonium chloride or ammoniumchloride or ammonium nitrate to the latex which causes the latex to gelwithin a relatively short and predeterminable time after it has beenadded to the latex, or by freezing the frothed or foamed latex andforcing a liquid or gas coagulant through the frozen latex as describedin United States Patent 2,432,353. The congealed cellular masg isvulcanized in the usual manner, for example, by heating the coagulatedlatex in amold or hot air oven ata vulcanizing temperature until thedesired vulcanization is obtained. (It is apparent that in themanufacture of foam rubber by the process of this invention the steps ofthe process through the step of vulcanizing the coagulated cellularlatex mass are the same as those normally employed heretofore in makingfoam rubber). h V After vulcanization the foam rubber preferably iswashed with water to remove water-soluble materials, such as soap, fromthe foam rubber before the foam rubber is treated with the aqueouscolloidal silica'dispersion. If the foam rubber has been coagulated byfreezing the frothed latex and forcing a liquid or gas coagulant throughthe frozen latex as described in United States Patent 2,432,353, thefoam rubber need not be driedbefore it is treated with the aqueouscolloidal silica dispersion, but if gelation of the frothed latex isaccomplished by using a delayed action coagulant, such as sodiumsilicofluoride, the vulcanized foam rubber should be dried in the usualmanner before attempting treatment of the foam rubber with the aquesouscolloidal silica dispersion. v

The vulcanized foam rubber is treated with the aqueous colloidal silicadispersion by impregnating or permeating the foam rubber, preferablythroughout its entire thickness, with the colloidal silica dispersion,for example, by immersing or dipping the foam rubber in a bath of theaqueous colloidal silica dispersion or by cascading or spraying theaqueous colloidal silica dispersion onto the foam rubber. The aqueouscolloidal silica dispersion used in this invention is an aqueousdispersion cornprising colloidal silica, commonly referred to as; asilica sol, to which may be added other materials for modifying the foamrubber. The silica particles may not be g and the weight present in thedispersion as anhydrous silicon dioxide I but may be in ahydrated formassociated. with various proportions of water. Such dispersionsfrequently are stabilized with a small amount of alkali to prevent theprecipitation of the silica in the form of a gel. Colloidal silicadispersions may be made in a variety of well known ways, severalprocesses for making such dispersions being described in United StatesPatent 2,574,902. 1 r

The aqueous colloidal silica dispersion desirably comprises about .5 to30 percent by weight colloidal silica, a dispersion having a silicacontent of about .5 to 20 percent by weight being preferred. Preferablysubstantially all of the silica particles in the dispersion have, aparticle size under 300 millimicrons and best results are obtained whenthe silica particles of the dispersion have an average particlesize ofless than about 25 mil-limic'rons and when the range of different sizesilica particles is relatively narrow. An aqueous dispersion ofcolloidal silica produced according to United States Patent 2,574,902has been found to be particularly satisfactory for use in thisinvention;

After the foam rubber has been treated with the colloidal silicadispersion, the foam rubber preferably is passed between pressure rollsto squeeze excess colloidal silica dispersion from the foam rubber, andthe foam rubber then is dried in the usual mariner such as in an airoven.

The foam rubber treated with the colloidal silica dispersion in theabove-described manner has a much higher compressionresistanceascompared to the'same foam rubber which has not been so treated. Otherphysical properties of the treated foam rubber are essentiallyunchanged. The reason for the increase in compression resistance of thefoam rubber is not understood.

If desired, a latex may be included in the aqueous colloidal silicadispersion, although preferably the solids content of the latex does notconstitute more than about 10 percent by weight of the aqueous colloidalsilica dispersion used for treating theifoam rubber. Any natural orsynthetic latices or blends thereof can be used for this purpose and thelatex should be compounded in the usual manner before being added to thedispersion. The addition' of a small amount of mono-ethyl amine to thelatex (one part by weight per parts by weight of latex usually'beingsufiicient) prevents the formation of floc when the latex is added tothe dispersion. The dispersion should be well agitated to preventmaterials compounded with the latex from settling out and to insure thatobjectionableflocculation of the latex does not occur inthe dispersion.

The invention is illustrated by'the following examples.

Example I Flat, cored, open-cell foam rubber automobile topper pads(used as a topping material over a spring frame foran automobileseat).about one and one-quarterinches thick were formed by thefreeze-coagulation process described in United States Patent 2,432,353from a blend oflatices containing equal proportions of a natural rubberlatex and a high solids butadiene-styrene latex (GR-S type No. X-667)..The vulcanized topper pads were washed in the usual manner to removewater-soluble materials such as soap from the foam rubber. The undried,washed topper pads were immersed in aqueous colloidal silica dispersionsof varying colloidal silica content, conveyed between squeeze rolls andthen dried in a circulating hot air oven. The compression resistance ofthe topper pads (when compressed to 75 percent of their original height)of the colloidal silica treated topper pads was determined and comparedwith the compression resistance and'weight of topper pads which had notbeen treatedwith a colloidal silica dispersion. The compressionresistance of the colloidal s ilica treated topper pads was muchsuperior to that of the untreated topper pads. he relationship betweenpercentincrease in compression resistance of the topper pads and thepercent increase in weight of the topper pads is shown by curve E ofFig. 1.

Example 2 Topperpads were formed and evaluated as in Example 1 exceptthat the topper pads were immersed in aqueous colloidal silicadispersions containing a compounded butadiene-styrene' latex (GR-S typeNo. X-667), the ratio of silica to latex solids being 50:50. The latexadded to the aqueous dispersions of colloidal silica had the followingcomposition:

The relationship between the percent increase in compression resistanceand the percent increase in weight of the topper pads formed inaccordance with this example is shown by curve D of Fig. 1.

Example 3 Topper pads were formed and evaluated as in Example 2 exceptthat the ratio of silica to latex solids in the dispersions was 25:75.The relationship between the percent increase in compression resistanceand the percent increase in weight of the topper pads formed inaccordance with this example is shown by curve C of Fig. 1.

Topper pads formed as in Example 1 except that they were treated withaqueous dispersions of the compounded butadiene-styrene latex used inthe immersion dispersions of Examples 2 and 3 instead of colloidalsilica dispersions, the latex being diluted with water to varyingconcentrations, also were evaluated. The relationship between thepercent increase in compression resistance and the percent increase inweight of the topper pads treated with the diluted latex is shown bycurve B in Fig. 1.

Curve A of Fig. 1 shows the percent increase in compression resistanceof topper pads (compressed to 75 percent of original height) obtained byincreasing the density of the foam rubber of the topper pads.

Referring to Fig. 1, it is apparent that the treatment of foam rubberwith an aqueous colloidal silica dispersion greatly improved thecompression resistance of the foam rubber and that the increase incompression resistance is not due merely to an increase in density(weight) of the foam rubber since the improveinentin compressionresistance realized is much greater than would occur by merelyincreasing the density of the foam rubber.

It has been found that the compression resistance of the foam rubber canbe increased further by repeated impregnations of the foam rubber withan aqueous colloidal silica dispersion, as illustrated by the followingexample, although the percentage increase in compression resistance onsuccessive dips may not be as great as obtained with the initialtreatment.

Example 4.

Samples of an open-cell foam rubber automobile door Weatherstrip wereimmersed in an aqueous colloidal silica dispersion percent by weighttotal solids) containing a compounded butadiene-styrene latex (GR-S typeNo. X-667), the ratio of silica to latex solids in the dispersion being50:50, and then were passed through squeeze rolls and dried for minutesof 210 F. The samples were immersed, squeezed and dried a second andthird time. The samples exhibited a weight increase of 7.6 percent andan increase in compression resistance of 27.4 percent after they hadbeen immersed, squeezed and dried once, and a weight increase of 21.1percent and an increase in compression resistance of 94.2 percent afterbeing immersed, squeezed and dried a third time (the compressionresistance was measured by determining the force in pounds required to.compress the thickness of a 12 inch length of the Weatherstrip under aninitial load of one pound a distance of 4; inch).

The compression resistance of a foam rubber treated with an aqueouscolloidal silica dispersion varies with the amount of compression(deflection) in a manner similar to that of a foam rubber which has notbeen treated with a colloidal silica dispersion, except that thecompression resistance of the colloidal silica treated foam rubber isgreater than that'of the untreated foam rubber, as illustrated by thefollowing example.

Example 5 The compression resistance of an untreated cored open-cellfoam rubber utility slab, 3% inches thick, was measured at increments of10 percent deflection of the original height of the slab, see .Fig. 2(untreated), the

.same slab of foam rubber then was immersed in an aqueous colloidalsilica dispersion (10 percent total solids) containing a compoundedbutadiene-styrene latex (GR-S type No. X-667), squeezed and dried, andthe compression resistance of the treated slab was measured for the sameincrements of deflection as the untreated foam rubber, see Fig. 2(treated). Referring to Fig. 2, it is seen that the curve for thetreated foam rubber slab is quite similar in shape to the curve for theuntreated foam rubber slab.

The percent increase in weight of the treated slab was 4.3 percent andthe present increase in compression resistance of the treated foamrubber as compared to the untreated foam rubber at the increments ofdeflection at which compression resistances were determined are as Asillustrated above and as shown in Fig. 2, the compression resistance ofthe treated foam rubber is greater than the compression resistance ofthe untreated foam rubber through at least a deflection of percent,which is close to the bottoming condition of foam rubber,

although it might be expected that the treatment of foam rubber withcolloidal silica would only be effective in the lower deflection rangeof 10 to 50 percent deflection where the rigidity of the cell walls ofthe foam rubber would be a major factor contributing to the compressionresistance.

It is clear that many modifications and variations of this invention maybe made without departing from the spirit and scope of the appendedclaims.

We claim:

1. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex, vulcanizing the congealed cellularmass to form an opencell foam rubber, and impregnating the vulcanizedfoam rubber with an aqueous dispersion comprising colloidal silica.

2. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delay action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, drying the foam rubber, and impregnating the dried vulcanizedfoam rubber with an aqueous dispersion comprising colloidal silica.

3. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delay action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, washing the foam rubber to remove water-soluble materials fromthe foam rubber, drying the washed foam rubber, and impregnating thedried vulcanized foam rubber with an aqueous dispersion comprisingcolloidal silica.

4. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delayed action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, washing the foam rubber to remove water-soluble materials fromthe foam rubber, drying the washed foam rubber, impregnating the driedvulcanized foam rubber with an aqueous dispersion comprising about .5 to30 percent by weight colloidal silica,'squeezing the foam rubber toremove any excess aqueous colloidal silica dis- .persion from the foamrubber, and drying the foam rubber.

5. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delayed action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, washing the foam rubber to remove water-soluble mate'- rialsfrom the foam rubber, drying the washed foam rubber, impregnating thedried vulcanized'foam rubber with an aqueous dispersion comprising about.5 to 20 percent by weight colloidal silica, squeezing the foam rubberto remove any excess aqueous colloidal silica dispersion from the foamrubber, and drying the foam rubber.

6. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delay action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, Washing the foam rubber to remove water-soluble materials fromthe foam rubber, drying the washed foam rubber, impregnating the driedvulcanized foam rubber with an aqueous dispersion comprising about .5 to30 percent by weight colloidal silica, substantially all of thecolloidal silica in the aqueous colloidal silica dispersion having aparticle size under 300 millimicrons, squeezing the foam rubber toremove any excess aqueous colloidal silica dispersion from the foamrubber, and drying the foam rubber.

7. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delayed action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, washing the foam rubber to remove water-soluble materials fromthe foam rubber, drying the washed foam rubber, impregnating the driedvulcanized foam rubber with an aqueous dispersion comprising about .5 to30 percent by weight colloidal silica, the average particle size ofcolloidal silica in the aqueous colloidal silica dispersion being lessthan about 25 millimicrons and substantially all of the colloidal silicain the aqueous colloidal silica dispersion having a particle size under300 millimicrons, squeezing the foam rubber to remove any excess aqueouscolloidal silica dispersion from the foam rubber, and drying the foamrubber.

8. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanzing thecongealed cellular mass to form an open-cell foam rubber, andimpreghating the vulcanized foam rubber with an aqueous dispersioncomprising colloidal silica.

9. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber,drying the foam rubber, and impregnating the dried vulcanized foamrubber with an aqueous dispersion comprising colloidal silica.

10. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber, andimpregnating the washed vulcanized foam rubber with an aqueousdispersion comprising colloidal silica.

11. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber,impregnating the washed vulcanized '8 foam rubber with an aqueousdispersion comprising about .5 to 30 percent by weight colloidal silica,squeezing the foam rubber to remove any excess aqueous colloidal silicadispersion from the foam rubber, and drying the foam rubber.

12. A process for making an open-cell foam rubber comprisingfoamingalatex, congealing the foamed latex by freezing it and then passingafluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber,impregnating the washed vulcanized foam rubber with an aqueousdispersion comprising about .5 to 20 percent by weight colloidal silica,squeezing the foam rubber to remove any excess aqueous colloidal silicadispersion from the foam rubber, and drying the foam rubber.

13. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by reezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber,impregnating the washed vulcanized foam rubber with an aqueousdispersion comprising about .5 to 30 percent by weight colloidal silica,substantially all of the colloidal silica in the aqueous colloidalsilica dispersion having a particle size under 300 millimicrons,squeezing the-foam rubber to remove any excess aqueous coltoioai silicadispersion from the foam rubber, and drying the foam rubber.

14. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, washing thefoam rubber to remove water-soluble materials from the foam rubber,impregnating the Washed vulcanized foam rubber with an aqueousdispersion comprising about .5 to 30 percent by weight colloidal silica,the average particle size of colloidal silica in the aqueous colloidalsilica dispersion being less than about 25 millimicrons andsubstantially all of the colloidal silica in the aqueous colloidalsilica dispersion having a particle size under 30G millimicrons,squeezing the foam rubber to remove any excess aqueous colloidal silicadispersion from the foam rubber, and drying the foam rubber.

15. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex, vulcanizing the congealed cellularmass to form an opencell foam rubber, and impregnating the vulcanizedfoam rubber with an aqueous dispersion comprising colloidal silica and alatex.

16. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delayed action coagulant,vulcanizing the congealed cellular mass to form an open-cell foamrubber, drying the foam rubber, and impregnating the dried vulcanizedfoam rubber with an aqueous dispersion comprising colloidal silica and alatex.

17. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex with a delayed action coagulant,vulcanizing the congealed cellular mass to form an open-cellfoam-rubber, drying the foam rubber, impregnating the dried vulcanizedfoam rubber with an aqueous dispersion comprising colloidal silica and alatex, said aqueous dispersion containing about .5 to 30 percent byweight colloidal silica and less than about 10 percent by weight latexsolids.

18. A process for making an open-cell foam rubber comprising foaming alatex, congealing the foamed latex by freezing it and then passing afluid coagulant through the frozen cellular mass, vulcanizing thecongealed cellular mass to form an open-cell foam rubber, andimpregnating the vulcanized foam rubber an aqueous disweight colloidalsilica and less than about 10 percent persion comprising colloidalsilica and; a latex. by weight latex solids. 19. A process for making anopen-cell foam rubber comprising foaming a latex, congealing the foamedlatex I References Cited in 116 file Of this patent by freezing it andthen passing a fluid'coagulant through 5 UNITED STATES PATENTS thefrozen cellular mass, vulcamzmg the congealed cellular mass to form anopen-cell foam rubber, and impreg- 2,200,850 Miserentino May 14, 1940nating the vulcanized foam rubber with an aqueous dis- 2,432,353 TalalayDec. 9, 1947 persion comprising colloidal silica and a latex, said aque-2,711,977 Butsch June 28, 1955 cus dispersion comprising about .5 to 30percent by 10 2,760,941 Iler et a1. Aug. 28. 1956 UNITED STATES PATENTOFFifiE CERTIFICATE OF CGRRQTION Patent No. 2,926 39O March 1, 1960 vAnselm Talalay et alr It is hereby certified that error appears in theprinted specification of the above numbered patent requiring correctionand that the said Letters Patent should read as corrected below.

Column 1, line 59, the formula should appear as shown below instead ofas in the patent:

"h=4(1 6) /P column 3, line 3, strike out ammonium chloride or"; column5, line 25, for "improved" read improves column 6, line 59,

and column 7, line 16, for 'delay", each occurrence read delayed Signedand sealed this 4th day of October 1960a (SEAL) Attest:

KARL H. AXLINE ROBERT C. WATSON Attesting Officer Commissioner ofPatents

1. A PROCESS FOR MAKING AN OPEN-CELL FOAM RUBBER COMPRISING FOAMING ALATEX, CONGEALING THE FOAMED LATEX, VULCANIZING THE CONGEALED CELLULARMASS TO FORM AN OPENCELL FOAM RUBBER, AND IMPREGNATING THE VULCANIZEDFOAM